It depends what you want.

I don't think there is a "cheap way" of making any pond that's going to last.
It's a lot of effort to build and ideally, I'd want one that requires little maintenance.

I'm a koi keeper with a 3000 gallon pool, but we also have a small "frog pond" next to it.

I'd recommend the following method of construction, for durability.

Make sure there are no tree roots anywhere near you intend to put your pond.
Use a bit of hosepipe to form the shape of your pond and then look at it from all angles to decide you've got it right, make any necessary adjustments.

Dig a three or four inch deep and six inch wide trench for a concrete collar, for your pond, use bits of wood for the shuttering, check the collar is perfectly level then fill with concrete.
Let it go off for a few days and then dig it out the pond.
With a collar you'll make less mess and won't tread the sides down while you dig it out. This way you could build one in the middle of your lawn if you so chose.
Make sure you include a short length of overflow polypipe in the collar to act as just that.

Line it with sand and then put some insulation down, carpet underlay is ideal.

Decide on some coping stones, bits of York stone or similar is ideal.
Use a good quality liner and lay it across the pool, put a few of the coping stones on the liner on top of the collar.

Start to fill the pool slowly, the weight of the water will slowly pull the liner down and stop wrinkles forming, the stones keeping the liner relatively taut, you'll have to watch the coping stones don't get dragged into the pool.
When it's full, trim off the surplus liner at a point half way across the collar.

Cement in the coping stones.

Let it go off and when dry, drain the pool to clear any cement debris from the pool, it doesn't do frogs any good.

There you have it. The pool is level and you can stand on the edge with no danger of the sides falling in.

This is the one as it was when I built 25 years ago.

http://img600.imageshack.us/img600/6499/10014s.jpg

I have had to replace the liner which got punctured about ten years ago, but that was easy enough, I just chiseled off each of the coping stones with one tap of a bolster chisel, removed the old liner and put in a new one and re-cemented the coping stones, a "non messy repair."

You will need to "trickle change" your pool from time to time with fresh water, but if you've arranged for the overflow to run to a soak-away or garden border, you can do this overnight without any bother.

Here it is last year, I've since moved the lamp, it's a bit overshadowed now by that acer palmatum, which is about eight feet wide now, but the frogs don't mind.

http://img96.imageshack.us/img96/1571/p1030210u.jpg